In recent years, container ships become larger and larger to increase the transport efficiency. The torsional rigidity of a container ship is lower than other type of ships, because the container ship has the large deck opening and large flare structure. Therefore, it is important to calculate the longitudinal ultimate strength with considering the torsional moment for the design of ships.

In the 1st report, the structure model test was carried out to clarify the effect of the torsional moment on the ultimate longitudinal strength of a container ship with deck opening. The 3D-FEA (Finite Element Analysis) were also carried out and the collapse behavior of the model was investigated in detail. But it requires large computational effort and cost to conduct 3D-FEA. Therefore, the simple and fast analysis to calculate the ultimate longitudinal strength with considering the torsional moment is needed. Thus, in the 2nd report, a new method of the progressive collapse analysis to calculate the ultimate longitudinal strength considering the torsional moment was developed by connecting the beam elements, of which the collapse of cross section is simulated by the Smith method, in the direction of ship length. The effect of the torsional moment was considered in the warping stresses and the yield strength of material. The effectiveness of the method was verified through comparison with the 3D-FEA of the test model.

In the present study, the calculation method for the torsional constant in consideration of the effect of bulkheads and side structures is proposed. The transverse bulkheads and the side structures prevent torsional deformation of ship's hull girder. Therefore, in this method, the original torsional constant is modified by considering the strain energy of the transverse bulkheads and the side structures. Finally, 3D-LFEA (Linear Finite Element Analysis) for the model with the U-shaped cross-section subjected to the torsional moment is carried out to clarify the validity of the 1D-LFEA considering the effect of the bulkhead and side structure.